The invention relates to a method and a device for regulating an intake pressure of an internal combustion engine, in particular diesel engine, having an exhaust gas turbocharger.
Internal combustion engines, such as for example diesel engines, are frequently equipped with exhaust gas turbochargers. They have a turbine which is driven by the exhaust gas and which is coupled to a compressor. The compressor compresses the intake air in order to increase an intake pressure in an intake line for the internal combustion engine, as a result of which, for example, an acceleration behaviour of the vehicle with the internal combustion engine is achieved and the consumption of energy is reduced.
However, the exhaust gas turbocharger cannot deliver sufficient air in every operating state of the internal combustion engine and therefore generate a sufficient intake pressure. In order to solve this problem, exhaust gas turbochargers with variable geometry have been proposed, in which, for example, guide vanes for turbines/compressors can be adjusted as a function of the respective operating state or operating data/parameters of the internal combustion engine. However, it is disadvantageous here that an exhaust gas turbocharger with variable geometry is costly and complex in terms of parts. Furthermore, it can be very maintenance-intensive, which increases the operating costs of a vehicle. In addition, it is also not always possible for an exhaust gas turbocharger with variable geometry to deliver the quantity of air required by the internal combustion engine. In particular in what is referred to as a non-steady-state range, such as for example acceleration, problems occur. If the exhaust gas turbocharger is optimized for such a non-steady-state range, it has a poor efficiency and an associated high level of fuel consumption in the steady-state range, for example when travelling at a constant velocity or with a constant engine speed.
Furthermore, piston engines such as diesel engines with an exhaust gas turbocharger have, for example, an operating state when accelerating which is referred to as “turbo lag”. Here, when the throttle is opened the internal combustion engine does not react by increasing the rotational speed until after a certain delay time in which no exhaust gas energy, that is to say an insufficient exhaust gas pressure, is available to drive the exhaust gas turbocharger and therefore no compressed intake air with corresponding intake pressure is available. In order to get around this turbo lag, solutions have been proposed which are described in German Laid-Open Patent Applications DE 10 2006 008 783 A1 and DE 10 2006 008 785 A1. Here, compressed air, for example from a compressed air accumulator, is fed in a controlled fashion into the intake line of the internal combustion engine in order to cover the intake air demand of the internal combustion engine when said demand is increased. This is carried out by means of a component which is arranged in the intake line between the compressor of the turbocharger or an intermediate cooler connected downstream in the direction of flow and the intake manifold, and said component has a compressed air port with a flow rate control device and a controlled flap. When compressed air is fed in through the flow rate control device, the controlled flap is closed with the effect that the compressed air does not flow into the compressor of the exhaust gas turbocharger counter to the intake direction but rather flows directed into the intake line. When the compressed air supply ends, this flap is opened again. There is no description of controlling the intake pressure of an internal combustion engine, in particular at an excessively high compressor pressure of the exhaust gas turbocharger.
The object of the present invention is therefore to make available a method and a device for regulating an intake pressure of an internal combustion engine, wherein the above disadvantages are overcome or significantly reduced and further advantages are obtained.
A basic idea of the invention is that an actuating element is provided in an actuating section in the intake line between the compressor of the exhaust gas turbocharger or a downstream intermediate cooler and the intake manifold of the internal combustion engine in order to influence the cross section of the intake line as a function of the intake pressure of the internal combustion engine.
This advantageously ensures that this actuating element reduces the cross section of the actuating section of the intake line if the compressor of the exhaust gas turbocharger delivers a quantity of air which is too large for the current operating state at an excessively high pressure. The intake pressure downstream of the actuating element in the direction of flow can therefore be influenced by the position of said actuating element, in particular as a function of the intake pressure which is measured with a suitable measuring device.
A method according to the invention for regulating an intake pressure of an internal combustion engine, in particular diesel engine, having an exhaust gas turbocharger whose compressor is connected to an intake line of the internal combustion engine via an actuating section which has an actuating element for changing a cross section of the actuating section, has the following method steps:
acquisition of the current intake pressure in the intake line of the internal combustion engine and of a compressor pressure of the compressor by means of pressure sensors;
comparison of the acquired current intake pressure and of the compressor pressure with setpoint values which correspond to current operating data of the internal combustion engine by a control unit, and generation of an actuating signal with said control unit on the basis of the comparison; and
changing of the cross section of the actuating section as a function of the current intake pressure, compressor pressure and the current operating data by adjusting the actuating element by the actuating signals generated by the control unit, in order to regulate the intake pressure of the internal combustion engine.
A further advantage is that either an exhaust gas turbocharger with a fixed geometry or an exhaust gas turbocharger with a variable geometry can be used, as a result of which the field of application of the invention is expanded.
In a preferred embodiment, the intake pressure is acquired by at least one pressure sensor downstream of the actuating element in the direction of flow. It is also preferred here that a compressor pressure is measured by a further pressure sensor which is arranged upstream of the actuating element in the direction of flow.
These pressure sensors can advantageously be arranged at a component, specifically the actuating section, which accommodates the actuating element. As a result, only a small amount of installation space is required.
The measured values which are acquired by the pressure sensors are received by the control unit and can be adapted to a specific format for further processing. They are compared with setpoint values which correspond to current operating parameters or operating data of the internal combustion engine. The current operating data are obtained by communicating with an engine control device of the internal combustion engine. The control unit can, for this purpose, also communicate directly with corresponding measuring means. The setpoint values which correspond to the current operating state of the internal combustion engine, for the respective intake pressure to be controlled, are acquired from the current operating data, for example on the basis of stored table values and/or computational algorithms, and are compared with the current measured values. The comparison yields a difference which is used to generate actuating signals. If the difference is equal to zero, no actuating signals are generated. The actuating signals are used to control an adjustment unit for the actuating element. These may be, for example, current, voltage, pulse sequence, etc.
In a further embodiment, the control unit is connected to measuring devices on the internal combustion engine which deliver data on, for example, pressure, mass flow rate, temperature, etc., which are significant not only for the control unit but also for the engine control device. The control unit can pass on these data to the engine control device to which it is connected, for example via a data bus. As a result, expenditure on cabling is saved, also allowing data to be transmitted more reliably.
By comparing the setpoint values which correspond to the current operating data with the current intake pressure values, the control unit adjusts the actuating element in order to reduce the cross section of the actuating section when the current intake pressure is too high. When the current intake pressure is too low, the actuating element is adjusted in order to increase the cross section of the actuating section. Simple regulation of the intake pressure of the internal combustion engine is therefore possible. An excessively high compressor pressure with an excessively high mass flow rate is easily reduced by making the cross section smaller through a corresponding, diminishing position of the actuating element which may be, for example, a flap.
In an alternative embodiment, when the current intake pressure is too low and the compressor pressure is too low, additional compressed air can be blown into the intake line, wherein the actuating element is adjusted under the control of the control unit in order to make the cross section of the actuating section smaller so as to prevent a backflow into the compressor. When the feeding in of compressed air ends, the actuating element is adjusted so as to make the cross section of the actuating section larger. For this purpose, the actuating section has, downstream of the actuating element in the direction of flow, an additional duct for the regulated, temporary feeding in of compressed air as a function of operating data of the internal combustion engine. Compressed air can also be fed in as a function of other operating data, for example in order to overcome the abovementioned turbo lag.
An inventive device for regulating an intake pressure of an internal combustion engine, in particular diesel engine, having an exhaust gas turbocharger, has the following:
an actuating section for connecting the intake line of the internal combustion engine to a compressor of the exhaust gas turbocharger;
an actuating element which is arranged in the actuating section and has an adjustment drive for changing a cross section of the actuating section;
a first pressure sensor for measuring a current compressor pressure of a compressor of the exhaust gas turbocharger;
a second pressure sensor for measuring the current intake pressure in the intake line of the internal combustion engine; and
a control unit for comparing measured data of the pressure sensors with setpoint values which correspond to current operating data of the internal combustion engine, and for generating actuating signals in order to adjust the actuating element with the adjustment drive in order to regulate the intake pressure as a function of the measured data of the pressure sensors and current operating data of the internal combustion engine. For particularly advantageous regulation, it is expedient if the actuating element can be adjusted by an adjustment drive in an infinitely variable fashion with position feedback. However, the setting positions of the actuating element can, of course, also be embodied in an incremental fashion.
In an alternative embodiment, there is provision that the actuating section has an additional duct for letting in compressed air. As a result, a combined, advantageous device for regulating the intake pressure for adapting it to the operating states of the internal combustion engine is provided, and the actuating section is provided as a fresh air line section of a device for supplying fresh air for the controlled blowing in of compressed air.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description when considered in conjunction with the accompanying drawings.